A grafted chloromethylated SEBS pervaporation membrane and its preparation method

Abstract

This invention discloses a grafted chloromethylated SEBS pervaporation membrane and its preparation method. Using block polymers as raw materials, the material undergoes quaternization modification. Through hydrophilic modification and control of the membrane's microphase separation structure, the membrane achieves a high pervaporation flux. Quaternized chain alkanes are grafted onto the side chains of styrene segments, imparting hydrophilicity to the membrane and enhancing the hydrophilic / hydrophobic microphase separation effect. A covalent crosslinking network is constructed between the segments using an olefin-thiol crosslinking method, giving the membrane good structural stability and mechanical strength. This dense membrane contains a large number of positively charged quaternary ammonium groups, which is beneficial for improving the membrane's ability to retain salt ions. Furthermore, its excellent microbial degradation ability makes it a potential membrane material for fields such as water electrolysis for hydrogen production, microbial fuel cells, and energy storage.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of organic polymer block polymer film materials, and relates to a grafted chloromethylated SEBS pervaporation membrane and a preparation method. BACKGROUND

[0002] Fresh water resource shortage is a problem that needs to be solved for the sustainable survival and development of human beings. Researchers turn their attention to brackish water (1-10 g L -1 ), seawater (35 g L -1 ), brine (75-150 g L -1 ) and wastewater, and other non-drinking water sources, and convert them into fresh water by removing salt and other pollutants in the water through efficient water treatment technology to solve the fresh water resource crisis. Currently, the commonly used desalination technologies are thermal desalination and membrane desalination. Thermal desalination refers to separating salt and water based on thermal evaporation and condensation, and commonly used are multi-stage flash evaporation (MSF), multi-effect distillation (MED) and vapor compression distillation (VC). Thermal desalination technology requires high energy consumption, large equipment investment and wide land occupation. Compared with thermal desalination, membrane desalination has attracted widespread attention due to its high operational stability, low chemical cost, easy control and environmental friendliness.

[0003] In membrane desalination, reverse osmosis technology is dominant. About 70% of the seawater desalination equipment in the world uses reverse osmosis technology. In the reverse osmosis process, mechanical pressure greater than the osmotic pressure difference between the two sides of the membrane is provided by the equipment to make water transfer from the concentrated solution side to the dilute solution side. The concentration gradient of the solutions on both sides of the membrane must be maintained within a suitable range. When the salt concentration is 350 g L -1 or even higher, the energy consumption required to realize the reverse osmosis process is high. Membrane distillation combines the advantages of membrane separation and traditional thermal-driven separation process, and utilizes the vapor pressure difference to selectively transfer volatile components in the preheated feed liquid through the membrane to remove non-volatile components (such as macromolecules, colloids and ions, etc.), so that the rejection rate can reach more than 99.9%, and low-grade waste heat generated in industrial processes can be used as its energy source, the required heat value cost is significantly reduced compared with traditional thermal desalination technology, and in addition, the mass transfer driving force is less affected by the salt concentration of the feed liquid, so it can handle high-concentration feed liquid, and therefore has become a new direction of attention by researchers in recent years. However, membrane distillation has the problem of membrane pore wetting during long-term operation, which limits its development and application. Compared with membrane distillation, pervaporation membrane desalination technology selects a hydrophilic semi-permeable membrane material, which has high solubility selectivity and permeability to water, and also has good rejection effect on volatile organic matter, and therefore has great application potential.

[0004] Currently, the performance of pervaporation desalination membrane materials is still constrained by the interplay between water molecule permeation rate, desalination selectivity, and mechanical strength. Most membrane materials exhibit low water permeability due to limitations imposed by the solubility and diffusion of water molecules within the membrane (Desalination, 2016, 387:46-60; Desalination, 2020, 474:114198). Extensively studied, highly hydrophilic membrane materials such as cellulose, polyvinyl alcohol, and chitosan exhibit good adsorption and dissolution properties for water molecules; however, their small free volume for water molecule transport results in a low water permeation rate. Furthermore, their limited charge repulsion of salt ions affects desalination selectivity; and the membrane materials' tendency to swell leads to low mechanical strength. Summary of the Invention

[0005] To address the aforementioned deficiencies in the existing technology, the present invention aims to provide a high-efficiency, simple, low-cost, and environmentally friendly grafted chloromethylated SEBS pervaporation membrane for seawater desalination and its preparation method. The pervaporation membrane material prepared by chemical modification of block polymers has high flux, high selectivity, and high stability, and can be used for freshwater production.

[0006] The present invention is achieved through the following technical solution.

[0007] According to one aspect of the present invention, a method for preparing a grafted chloromethylated SEBS pervaporation membrane is provided, comprising:

[0008] a. Prepare polymer solution A by mixing 5-10 parts by mass of block polymer and add 10-20 parts by chloromethylation reagent and stir to dissolve.

[0009] The reaction is carried out under ice-water bath conditions with the addition of 50-60 parts of trimethylchlorosilane and 15-25 parts of catalyst A;

[0010] The product was obtained by precipitating with methanol / water mixture, and then purified and dried to obtain the chloromethylated product (SEBS@CH2Cl);

[0011] b. Prepare polymer solution B by mixing 25-30 parts of the product (SEBS@CH2Cl); add 60-70 parts of monomer, 2-5 parts of catalyst B, and 3-6 parts of ligand, and mix and dissolve.

[0012] Add 1-5 parts of reducing agent to react in a liquid nitrogen vacuum atmosphere;

[0013] The product was obtained by methanol precipitation and dried to obtain the polystyrene graft product SEBS-g-PSt.

[0014] c. Prepare polymer solution C by mixing 5-10 parts of graft product with 10-20 parts of chloromethylation reagent and stirring to dissolve.

[0015] The reaction is carried out under ice-water bath conditions with the addition of 50-60 parts of trimethylchlorosilane and 15-25 parts of catalyst A;

[0016] The product was obtained by methanol / water precipitation, and then purified and dried to obtain the chloromethylated graft product (SEBS-g-PSt@CH2Cl);

[0017] d. Prepare a casting solution by preparing the chloromethylated graft product (SEBS-g-PSt@CH2Cl), let it stand, and then degas it under vacuum;

[0018] The casting solution was scraped onto the substrate, shaped at room temperature, vacuum dried, and the chloromethylated grafted membrane was removed in water and dried.

[0019] e. The chloromethylated grafted membrane is reacted with a quaternizing agent and immersed in an alkaline solution to form a grafted chloromethylated SEBS pervaporation membrane.

[0020] According to another aspect of the present invention, a method for preparing a grafted chloromethylated SEBS pervaporation membrane is provided, comprising:

[0021] a. Prepare polymer solution A by mixing 5-10 parts by mass of block polymer and add 10-20 parts by chloromethylation reagent and stir to dissolve.

[0022] The reaction is carried out under ice-water bath conditions with the addition of 50-60 parts of trimethylchlorosilane and 15-25 parts of catalyst A;

[0023] The product was obtained by precipitating with methanol / water mixture, and then purified and dried to obtain the chloromethylated product (SEBS@CH2Cl);

[0024] b1. Prepare a polymer solution D by mixing 75-85 parts of the chloromethylated product (SEBS@CH2Cl) and reacting it with 15-25 parts of alkylamine reagent in a nitrogen atmosphere. Cast the mixture onto a substrate, allow it to evaporate into a film, dry it, immerse it in deionized water, remove the film and dry it to obtain a grafted chloromethylated SEBS pervaporation membrane.

[0025] According to another aspect of the present invention, a method for preparing a grafted chloromethylated SEBS pervaporation membrane is provided, comprising:

[0026] a. Prepare polymer solution A by mixing 5-10 parts by mass of block polymer and add 10-20 parts by chloromethylation reagent and stir to dissolve.

[0027] The reaction is carried out under ice-water bath conditions with the addition of 50-60 parts of trimethylchlorosilane and 15-25 parts of catalyst A;

[0028] The product was obtained by precipitating with methanol / water mixture, and then purified and dried to obtain the chloromethylated product (SEBS@CH2Cl);

[0029] b2. Prepare a polymer solution E by mixing 79-83 parts of chloromethylated product (SEBS@CH2Cl), add 14-16 parts of allylamine reagent and 3-5 parts of crosslinking agent, cast the mixture onto a substrate, and graft the chloromethylated SEBS pervaporation membrane after the membrane is shaped.

[0030] Preferably, the block polymer is polystyrene-(ethylene / butene)-styrene or styrene.

[0031] Preferably, the chloromethylating agent is chloromethyl ether, trioxymethylene, paraoxymethylene, or methylal.

[0032] Preferably, catalyst A is anhydrous zinc chloride, anhydrous ferric chloride, anhydrous aluminum chloride, or anhydrous tin tetrachloride.

[0033] Preferably, catalyst B is copper chloride, copper bromide, nickel chloride, ferric chloride hexahydrate, or nickel chloride hexahydrate.

[0034] Preferably, the monomer is styrene or maleic anhydride.

[0035] Preferably, the ligand is iminodiacetic acid, tris[2-(dimethylamino)ethyl]amine, triphenylphosphine, or tri-n-butylamine.

[0036] Preferably, the reducing agent is tin(II) 2-ethylhexanoate or ascorbic acid.

[0037] Preferably, the solvent for the casting solution is toluene, chloroform, tetrahydrofuran, N-methylpyrrolidone, or N,N-dimethylformamide.

[0038] Preferably, the quaternizing agent is a trimethylamine solution, a triethylamine solution, or a tributylamine solution.

[0039] Preferably, the substrate is glass, polytetrafluoroethylene, polyethyleneimine filter membrane, polysulfone filter membrane, polyethersulfone filter membrane, nylon filter membrane, polyacrylonitrile filter membrane, or cellulose acetate filter membrane.

[0040] Preferably, the alkylamine reagent is N,N-dimethylbutylamine, N,N-dimethyloctylamine, N,N-dimethyldodecylamine, or N,N-dimethyl-1-hexadecylamine.

[0041] Preferably, the allylamine reagent is diallylamine, triallylamine, N,N-dimethylallylamine, or N-methylallylamine.

[0042] Preferably, the crosslinking agent is o-phenyl dithiol, 1,4-phenyl-dithiol, biphenyl-4,4′-dithiol, 1,5-pentanedithiol, 1,6-hexanedithiol or 3,6-dioxo-1,8-octanedithiol.

[0043] In steps a and c, the reaction is carried out under ice-water bath conditions for 10–60 min, and then the reaction is carried out at 25–55 °C for 6–24 h after removing the ice-water bath.

[0044] In step b, after purging with nitrogen, the mixture is slowly heated to 80–120°C and a reducing agent is added; the reaction is carried out at 80–120°C in a nitrogen atmosphere for 6–12 hours.

[0045] In step b1, the grafting reaction is carried out at 25–55°C for 6–48 hours;

[0046] In step b2, the grafting reaction is carried out at 25–55°C for 6–48 h; and the crosslinking reaction is carried out at 100–150°C for 3–12 h.

[0047] In another aspect, the present invention provides a grafted chloromethylated SEBS pervaporation membrane prepared by the method described above.

[0048] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0049] 1. This invention leverages the structural advantages of SEBS block polymers and the prerequisite factors for quaternization hydrophilic modification. Using SEBS as a membrane-forming raw material, its monomeric structural differences give it excellent comprehensive properties, such as thermal and chemical stability and film-forming properties. Furthermore, its main chain does not contain CO bonds, preventing chain breakage under OH- attack, thus exhibiting excellent alkali resistance and suitability for treating acidic and alkaline saline solutions at certain high temperatures. The chloromethylation method in step a introduces chloromethyl sites into SEBS that can be used for subsequent quaternization modification. This method is greener, safer, and less expensive than traditional synthesis methods, making it suitable for large-scale applications.

[0050] 2. This invention, based on membrane permeability, uses the chloromethyl product of SEBS as a raw material and employs steps b, c, d, and e to graft more styrene monomers into SEBS. Through secondary chloromethylation and quaternization modification, the number of hydrophilic quaternary ammonium groups within the membrane is increased. The hydrophilic polystyrene blocks and hydrophobic ethylene / butene blocks aggregate to form hydrophilic and hydrophobic regions, respectively, generating a microphase separation structure, thereby forming nanochannels conducive to water transport. The hydrophilic modification and regulation of the membrane's microphase separation structure jointly enhance the water molecule transport performance within the membrane, enabling the membrane to achieve a high pervaporation flux. Simultaneously, the increased number of rigid benzene rings helps to regulate the internal structure of the membrane, improving its mechanical strength and maintaining a high salt rejection capacity.

[0051] 3. This invention, based on the physicochemical structure and reaction conditions of the pervaporation membrane, uses the chloromethyl product of SEBS as a raw material and replaces steps b, c, d, and e with step b1. Long side chains containing hydrophilic quaternary ammonium groups are introduced in one step at the chloromethyl sites of the styrene block via side-linking. By generating hydrophilic quaternary ammonium groups in situ on the side chains, the membrane's permeability to water molecules is improved, and a microphase separation structure is formed to regulate the diffusion performance of water molecules within the membrane. Simultaneously, the introduction of flexible hydrophilic quaternary ammonium chains increases the free volume of the membrane, indirectly increasing the space for water molecule transport within the membrane. Furthermore, the long hydrophobic chains contained in the grafted side chains make the hydrophilic / hydrophobic microphase separation structure of the membrane more pronounced. Hydrophobic regions within the membrane accelerate the aggregation to form continuous, large-area hydrophobic water zones, while hydrophilic regions aggregate to form equally large continuous hydrophilic water zones, further promoting water molecule transport within the membrane and enhancing the membrane's pervaporation desalination performance. In addition, the introduction of long chains enhances the flexibility of SEBS, preventing gelation during the reaction process.

[0052] 4. This invention, based on the mechanical strength and stability factors of pervaporation membranes, uses the chloromethyl product of SEBS as a raw material and replaces steps b, c, d, and e with step b2. Hydrophilic quaternary ammonium groups are introduced in one step by linking tertiary amine groups and double bonds on the sides. Simultaneously, a crosslinking agent containing thiol and ether bonds is introduced, and the crosslinking structure is designed based on the olefin-thiol crosslinking reaction mechanism in click chemistry. The click crosslinking reaction method is simple and convenient. The crosslinking reaction improves the dimensional stability, mechanical properties, and swelling resistance of the membrane material. Furthermore, the ether bonds in the crosslinking agent structure make the crosslinking chain flexible, thus compensating for the loss of hydrophilicity due to the crosslinking structure. A continuous channel for water molecules to pass through is opened in the crosslinking network. Introducing a crosslinking structure containing special functional groups can circumvent the mutual constraints between membrane permeability and salt rejection capacity, improving the "trade-off" effect between the two.

[0053] 5. Based on the actual pollution of industrial brine, this invention introduces positively charged quaternary ammonium groups through quaternization modification. The membrane prepared by casting has a dense, non-porous surface. This dense surface and abundant positively charged quaternary ammonium groups ensure the retention of salt ions through size sieving and charge repulsion, guaranteeing high desalination selectivity. Furthermore, the positively charged quaternary ammonium groups can suppress the presence of calcium in the feed solution. 2+ Mg 2+ The adsorption and deposition of hydroxides on the membrane surface alleviates membrane fouling. The membrane surface prepared by this invention contains a large number of quaternary ammonium groups and free hydroxide ions, which can effectively prevent microbial degradation of the membrane surface and weaken the activity of microorganisms, thus helping it to maintain a highly efficient and stable operating state when treating natural water bodies containing microorganisms. Attached Figure Description

[0054] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute an undue limitation of the invention. In the drawings:

[0055] Figure 1 Image of SEBS sample;

[0056] Figure 2 The image shows the physical specimen of the grafted chloromethylated SEBS pervaporation membrane prepared in Example 4.

[0057] Figure 3 For SEBS H 1 NMR spectrum;

[0058] Figure 4 H for SEBS@CH2Cl 1 NMR spectrum;

[0059] Figure 5 Schematic diagram of the crosslinking structure of CL-SEBS constructed with different crosslinking agents. Detailed Implementation

[0060] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0061] An embodiment of the present invention provides a method for preparing a polystyrene-grafted chloromethylated SEBS pervaporation membrane with high polystyrene content, comprising the following steps:

[0062] a. Dissolve 5-10 parts of block polymer (polystyrene-(ethylene / butene)-styrene or styrene) in chloroform to prepare a polymer solution A with a mass fraction of 0.5-10%. Then add 10-20 parts of chloromethylating agent (chloromethyl ether, paraformaldehyde, polyoxymethylene, or methylal) and stir evenly to ensure complete dissolution. Add 50-60 parts of trimethylchlorosilane and 15-25 parts of catalyst A (anhydrous zinc chloride, anhydrous ferric chloride, anhydrous aluminum chloride, or anhydrous tin tetrachloride) dropwise under an ice-water bath at -5 to 0°C. React for 10-60 minutes under ice-water bath conditions, then remove the ice-water bath and allow the reaction to proceed at 25-55°C for 6-24 hours. Subsequently, add a 10-20% methanol / water mixture to terminate the reaction. Pour the mixture into methanol to obtain the precipitate. Purify the product by performing 1-5 cycles of chloroform dissolution-methanol precipitation. Finally, the obtained chloromethylated product (SEBS@CH2Cl) was placed in a vacuum oven and dried at 25–50 °C for 24–72 h.

[0063] b. Dissolve 25-30 parts of the product (SEBS@CH2Cl) in toluene to prepare a polymer solution B with a mass fraction of 0.5-10%. Then, sequentially add 60-70 parts of monomer (styrene, maleic anhydride), 2-5 parts of catalyst B (copper chloride, copper bromide, nickel chloride, ferric chloride hexahydrate or nickel chloride hexahydrate), and 3-6 parts of ligand (iminodiacetic acid, tris[2-(dimethylamino)ethyl]amine, triphenylphosphine or tri-n-butylamine), stirring until completely dissolved. Freeze in a liquid nitrogen atmosphere and continuously evacuate and purge with nitrogen 1-5 times. Then, slowly heat to 80-120°C, add 1-5 parts of reducing agent (tin(II) 2-ethylhexanoate or ascorbic acid), and react at 80-120°C under a nitrogen atmosphere for 6-12 hours. Precipitate the product after the reaction with 100-300% methanol to obtain the final product, then wash with methanol 1-3 times. Finally, the product was placed in an oven and vacuum dried at 25–50°C for 24–72 h to obtain the polystyrene graft product SEBS-g-PSt.

[0064] c. Dissolve 5-10 parts of the grafted product in chloroform to prepare a polymer solution C with a mass fraction of 0.5-10%. Then add 10-20 parts of a chloromethylating agent (chloromethyl ether, paraformaldehyde, polyformaldehyde, or methylal) and stir thoroughly until fully dissolved. Under ice-water bath conditions (-5 to 0°C), add 50-60 parts of trimethylchlorosilane and 15-25 parts of a catalyst (anhydrous zinc chloride, anhydrous ferric chloride, anhydrous aluminum chloride, or anhydrous tin tetrachloride) dropwise. After reacting for 10-60 minutes under ice-water bath conditions, remove the ice-water bath and allow it to react fully at 25-55°C for 6-24 hours. Subsequently, add a methanol / water mixture with a mass fraction of 10-20% to terminate the reaction. Pour the mixture into methanol to obtain the precipitated product. The product is purified by 1-5 cycles of chloroform dissolution-methanol precipitation. Finally, the obtained product (SEBS-g-PSt@CH2Cl) was placed in a vacuum oven and dried at 25–50 °C for 24–72 h.

[0065] d. Prepare a casting solution with a mass fraction of 1-15% by mixing the product (SEBS-g-PSt@CH2Cl) and the casting solution solvent (toluene, chloroform, tetrahydrofuran, N-methylpyrrolidone, or N,N-dimethylformamide). Allow it to stand until it dissolves and reaches a certain viscosity and flowability. Vacuum the casting solution for 5-30 minutes to completely degas it. Then, use a doctor blade with a thickness of 0.3-1 mm to coat the substrate (glass, polytetrafluoroethylene (PTFE) sheet, polyethyleneimine (PEI) filter membrane, polysulfone filter membrane, polyethersulfone filter membrane, nylon filter membrane, polyacrylonitrile filter membrane, cellulose acetate filter membrane). Set the membrane at room temperature for 1-3 hours, then place the sheet in a vacuum oven and vacuum dry at 80°C for 12-72 hours to allow the solvent to completely evaporate. Finally, immerse the sheet in deionized water to remove the membrane (SEBS-g-PSt@CH2Cl), dry it, and store it for later use.

[0066] e. Cut the dried SEBS-g-PSt@CH2Cl membrane to a suitable size, add a quaternizing agent (trimethylamine solution, triethylamine solution, or tributylamine solution) at a mass ratio of 1:20, immerse the membrane in the quaternizing agent and seal it, allowing it to react at room temperature for 12–48 h. After the reaction is complete, immerse the membrane in 1 mol L... -1 In alkaline solutions (sodium hydroxide solution, potassium hydroxide solution), Cl is completed. - and OH - After the exchange of molecules, the membrane is removed and dried to obtain the grafted chloromethylated SEBS pervaporation membrane.

[0067] Grafted polystyrene (SEBS) refers to the process of grafting styrene monomers onto the side ends of the SEBS backbone using SEBS macromolecules as initiators via atom transfer radical polymerization to form long polystyrene chains with varying degrees of polymerization.

[0068] Because styrene monomers contain benzene rings that can be hydrophilically modified through quaternization, grafted styrene monomers can introduce more chloromethyl sites into SEBS materials through chloromethylation post-treatment. These chloromethyl sites are converted into quaternary ammonium groups, which can enhance the membrane's water permeability and facilitate the rapid transport of water molecules within the membrane at low energy barriers. Furthermore, the differences in hydrophilic / hydrophobic properties between different blocks of SEBS lead to the formation of continuous nanoscale hydrophilic water zones within the membrane, facilitating water molecule transport and enhancing water molecule diffusion within the membrane. Simultaneously, the introduction of more benzene rings helps improve the membrane's mechanical strength, regulates the internal structure, and enables the membrane to achieve high pervaporation water flux while maintaining high salt rejection capacity.

[0069] The present invention will be further illustrated below with reference to specific embodiments.

[0070] Example 1

[0071] a. Dissolve 8 parts of polystyrene-(ethylene / butene)-styrene in chloroform to prepare a 10% polymer solution A. Then add 15 parts of chloromethyl ether and stir evenly. Add 57 parts of trimethylchlorosilane and 20 parts of anhydrous zinc chloride dropwise in an ice-water bath at -5 to 0°C. After reacting for 40 min in the ice-water bath, remove the ice-water bath and react at 35°C for 20 h. Add 15% methanol / water solution and pour the mixture into methanol to obtain a precipitate. Purify the precipitate by 4 cycles of chloroform dissolution-methanol precipitation and dry at 40°C for 48 h to obtain the chloromethylated product (SEBS@CH2Cl).

[0072] b. Dissolve 26 parts of the product (SEBS@CH2Cl) in toluene to prepare a 10% polymer solution B; add 64 parts of styrene, 2.2 parts of copper chloride and 5.2 parts of iminodiacetic acid sequentially, stir to dissolve, freeze in liquid nitrogen atmosphere and continuously evacuate and purge nitrogen 3 times, heat to 100°C, add 2.6 parts of tin(II) 2-ethylhexanoate, react at 100°C in nitrogen atmosphere for 8 hours; precipitate the reaction product with 200% methanol to obtain the product, wash twice with methanol, and vacuum dry at 35°C for 48 hours to obtain the polystyrene graft product SEBS-g-PSt.

[0073] c. Dissolve 8 parts of the grafted product in chloroform to prepare a 5% polymer solution C. Add 15 parts of chloromethyl ether and stir to dissolve. Add 57 parts of trimethylchlorosilane and 20 parts of anhydrous zinc chloride dropwise in an ice-water bath (-5 to 0℃). After reacting for 40 min in the ice-water bath, remove the ice-water bath and react at 35℃ for 12 h. Add 15% methanol / water solution and pour the mixture into methanol to obtain the precipitated product. Purify the product by performing a chloroform dissolution-methanol precipitation process four times, and dry it in a vacuum oven at 40℃ for 60 h to obtain the product (SEBS-g-PSt@CH2Cl).

[0074] d. Prepare a 10% (w / w) casting solution by mixing the product (SEBS-g-PSt@CH2Cl) with toluene. Allow it to stand until it reaches a certain viscosity and flowability. Vacuum for 20 minutes to degas the solution. Apply the solution to a glass or PTFE plate using a doctor blade. Set the film at room temperature for 2 hours, then vacuum dry at 80°C for 48 hours. Immerse the plate in deionized water to remove the film (SEBS-g-PSt@CH2Cl) and dry it.

[0075] e. Cut the dried SEBS-g-PSt@CH2Cl membrane, add trimethylamine solution at a mass ratio of 1:20, seal, and react at room temperature for 24 hours; then immerse the membrane in 1 mol L⁻¹ water. -1 The membrane was removed and dried in a sodium hydroxide solution to obtain a grafted chloromethylated SEBS pervaporation membrane.

[0076] Example 2

[0077] a. Dissolve 5 parts of styrene in chloroform to prepare a polymer solution A with a mass fraction of 8%. Then add 15 parts of trioxymethylene and stir evenly. Add 60 parts of trimethylchlorosilane and 15 parts of anhydrous ferric chloride dropwise in an ice-water bath at -5 to 0°C. After reacting for 50 min in the ice-water bath, remove the ice-water bath and react at 25°C for 18 h. Add 10% methanol / water solution and pour the mixture into methanol to obtain a precipitate. Purify the precipitate by two cycles of chloroform dissolution-methanol precipitation and dry at 25°C for 72 h to obtain the chloromethylated product (SEBS@CH2Cl).

[0078] b. Dissolve 25 parts of the product (SEBS@CH2Cl) in toluene to prepare a polymer solution B with a mass fraction of 8%; add 65 parts of styrene, 2 parts of copper bromide and 3 parts of tris[2-(dimethylamino)ethyl]amine sequentially, stir to dissolve, freeze in liquid nitrogen atmosphere and continuously evacuate and purge nitrogen 3 times, heat to 80°C, add 5 parts of ascorbic acid, and react at 80°C in nitrogen atmosphere for 6-12 h; precipitate the reaction product with 150% methanol to obtain the product, wash with methanol 3 times, and vacuum dry at 25°C for 72 h to obtain the polystyrene graft product SEBS-g-PSt.

[0079] c. Dissolve 10 parts of the grafted product in chloroform to prepare a 10% polymer solution C. Add 20 parts of paraformaldehyde and stir to dissolve. Add 50 parts of trimethylchlorosilane and 20 parts of anhydrous ferric chloride dropwise in an ice-water bath (-5 to 0℃). After reacting for 30 min in the ice-water bath, remove the ice-water bath and react at 30℃ for 20 h. Add 10% methanol / water solution and pour the mixture into methanol to obtain the precipitated product. Purify the product by two chloroform dissolution-methanol precipitation processes, and dry it in a vacuum oven at 50℃ for 24 h to obtain the product (SEBS-g-PSt@CH2Cl).

[0080] d. Prepare a 5% (w / w) casting solution by mixing the product (SEBS-g-PSt@CH2Cl) with chloroform. Allow it to stand until it reaches a certain viscosity and flowability. Vacuum for 30 minutes to degas the solution. Coat the membrane onto a polyethyleneimine (PEI) filter membrane using a doctor blade. Set the membrane at room temperature for 1.5 hours, then vacuum dry it at 80°C for 12 hours. Immerse the plate in deionized water to remove the membrane (SEBS-g-PSt@CH2Cl) and dry it.

[0081] e. Cut the dried SEBS-g-PSt@CH2Cl membrane, add triethylamine solution (quaternizing agent) at a mass ratio of 1:20, seal, and react at room temperature for 18 hours; then immerse the membrane in 1 mol L... -1The membrane is removed and dried in sodium hydroxide solution or potassium hydroxide solution to obtain the grafted chloromethylated SEBS pervaporation membrane.

[0082] Example 3

[0083] a. Dissolve 6 parts of polystyrene-(ethylene / butene)-styrene in chloroform to prepare a 2% (w / w) polymer solution A. Then add 12 parts of paraformaldehyde or methyl acetal, stir evenly, and add 55 parts of trimethylchlorosilane and 17 parts of anhydrous aluminum chloride dropwise in an ice-water bath at -5 to 0°C. After reacting for 60 min in the ice-water bath, remove the ice-water bath and react at 25°C for 24 h. Add 20% methanol / water solution, pour the mixture into methanol to obtain a precipitate, and purify it by five cycles of chloroform dissolution-methanol precipitation. Dry at 30°C for 24 h to obtain the chloromethylated product (SEBS@CH2Cl).

[0084] b. Dissolve 30 parts of the product (SEBS@CH2Cl) in toluene to prepare a 3% polymer solution B; add 60 parts of maleic anhydride, 5 parts of nickel chloride and 3 parts of triphenylphosphine sequentially, stir to dissolve, freeze in liquid nitrogen atmosphere and continuously evacuate and purge nitrogen once, heat to 90°C, add 2 parts of ascorbic acid, and react at 90°C in nitrogen atmosphere for 6 hours; precipitate the reaction product with 300% methanol to obtain the product, wash with methanol 3 times, and dry under vacuum at 50°C for 24 hours to obtain the polystyrene graft product SEBS-g-PSt.

[0085] c. Dissolve 5 parts of the grafted product in chloroform to prepare a polymer solution C with a mass fraction of 8%. Add 10 parts of paraformaldehyde and stir to dissolve. Add 60 parts of trimethylchlorosilane and 25 parts of anhydrous aluminum chloride dropwise in an ice-water bath (-5 to 0℃). After reacting for 10 min in the ice-water bath, remove the ice-water bath and react at 55℃ for 6 h. Add 20% methanol / water solution and pour the mixture into methanol to obtain the precipitated product. Purify the product by a single chloroform dissolution-methanol precipitation process, and dry it in a vacuum oven at 25℃ for 72 h to obtain the product (SEBS-g-PSt@CH2Cl).

[0086] d. Prepare a casting solution with a mass fraction of 15% by mixing the product (SEBS-g-PSt@CH2Cl) and tetrahydrofuran. Allow it to stand until it reaches a certain viscosity and flowability. Vacuum for 5 minutes to degas the solution. Apply the solution to a polysulfone filter membrane using a doctor blade. Set the membrane at room temperature for 3 hours, then vacuum dry it at 80°C for 36 hours. Immerse the plate in deionized water to remove the membrane (SEBS-g-PSt@CH2Cl) and dry it.

[0087] e. Cut the dried SEBS-g-PSt@CH2Cl membrane, add tributylamine solution (quaternizing agent) at a mass ratio of 1:20, seal, and react at room temperature for 12 hours; then immerse the membrane in 1 mol L... -1 The membrane was removed and dried in a potassium hydroxide solution to obtain a grafted chloromethylated SEBS pervaporation membrane.

[0088] Example 4

[0089] a. Dissolve 10 parts of polystyrene-(ethylene / butene)-styrene in chloroform to prepare a 5% polymer solution A. Then add 18 parts of methylal and stir evenly. Add 50 parts of trimethylchlorosilane and 22 parts of anhydrous tin tetrachloride dropwise in an ice-water bath at -5 to 0°C. After reacting for 30 min in the ice-water bath, remove the ice-water bath and react at 50°C for 22 h. Add 15% methanol / water solution and pour the mixture into methanol to obtain a precipitate. Purify the precipitate by two chloroform dissolution-methanol precipitation processes and dry at 45°C for 36 h to obtain the chloromethylated product (SEBS@CH2Cl).

[0090] b. Dissolve 25 parts of the product (SEBS@CH2Cl) in toluene to prepare a 4% polymer solution B; add 69 parts of styrene, 2 parts of ferric chloride hexahydrate and 3 parts of tri-n-butylamine sequentially, stir to dissolve, freeze in liquid nitrogen atmosphere and continuously evacuate and purge with nitrogen 5 times, heat to 120°C, add 1 part of tin(II) 2-ethylhexanoate, react at 90°C and in nitrogen atmosphere for 12 h; precipitate the reaction product with 100% methanol to obtain the product, wash twice with methanol, and dry under vacuum at 45°C for 36 h to obtain the polystyrene graft product SEBS-g-PSt.

[0091] c. Dissolve 7 parts of the grafted product in chloroform to prepare a 3% polymer solution C. Add 20 parts of methyl acetal and stir to dissolve. Add 58 parts of trimethylchlorosilane and 15 parts of anhydrous tin tetrachloride dropwise in an ice-water bath (-5 to 0℃). After reacting for 60 min in the ice-water bath, remove the ice-water bath and react at 25℃ for 24 h. Add 10% methanol / water solution and pour the mixture into methanol to obtain the precipitated product. Purify the product by performing a chloroform dissolution-methanol precipitation process 5 times, and dry it in a vacuum oven at 40℃ for 36 h to obtain the product (SEBS-g-PSt@CH2Cl).

[0092] d. Prepare a 1% (w / w) casting solution from the product (SEBS-g-PSt@CH2Cl) and N-methylpyrrolidone. Allow it to stand until it reaches a certain viscosity and flowability. Vacuum for 20 minutes to degas the solution. Apply the solution to a nylon filter membrane using a doctor blade. Set the membrane at room temperature for 2 hours, then vacuum dry it at 80℃ for 72 hours. Immerse the plate in deionized water to remove the membrane (SEBS-g-PSt@CH2Cl) and dry it.

[0093] e. Cut the dried SEBS-g-PSt@CH2Cl membrane, add quaternizing reagent (trimethylamine solution, triethylamine solution, or tributylamine solution) at a mass ratio of 1:20, seal, and react at room temperature for 48 hours; immerse to 1 mol L -1 The membrane was removed and dried in a sodium hydroxide solution to obtain a grafted chloromethylated SEBS pervaporation membrane.

[0094] Example 5

[0095] a. Dissolve 7 parts of polystyrene-(ethylene / butene)-styrene in chloroform to prepare a 0.5% polymer solution A. Then add 10 parts of chloromethyl ether and stir evenly. Add 58 parts of trimethylchlorosilane and 25 parts of anhydrous ferric chloride dropwise in an ice-water bath at -5 to 0°C. After reacting for 10 minutes in the ice-water bath, remove the ice-water bath and react at 55°C for 6 hours. Add 20% methanol / water solution and pour the mixture into methanol to obtain a precipitate. Purify the precipitate by three cycles of chloroform dissolution-methanol precipitation and dry at 50°C for 60 hours to obtain the chloromethylated product (SEBS@CH2Cl).

[0096] b. Dissolve 25 parts of the product (SEBS@CH2Cl) in toluene to prepare a polymer solution B with a mass fraction of 0.5%; add 62 parts of maleic anhydride, 3 parts of nickel chloride hexahydrate and 6 parts of tri-n-butylamine in sequence, stir to dissolve, freeze in liquid nitrogen atmosphere and continuously evacuate and purge with nitrogen 3 times, heat to 110°C and add 4 parts of 2-ethylhexanoate tin(II), react at 115°C and in nitrogen atmosphere for 7 h; precipitate the reaction product with 150% methanol to obtain the product, wash twice with methanol, and dry under vacuum at 50°C for 60 h to obtain the polystyrene graft product SEBS-g-PSt.

[0097] c. Dissolve 6 parts of the grafted product in chloroform to prepare a 0.5% polymer solution C. Add 19 parts of chloromethyl ether and stir to dissolve. Add 60 parts of trimethylchlorosilane and 15 parts of anhydrous ferric chloride dropwise in an ice-water bath (-5 to 0℃). After reacting for 30 min in the ice-water bath, remove the ice-water bath and react at 50℃ for 12 h. Add 10% methanol / water solution and pour the mixture into methanol to obtain the precipitated product. Purify the product by three chloroform dissolution-methanol precipitation processes, and dry it in a vacuum oven at 50℃ for 48 h to obtain the product (SEBS-g-PSt@CH2Cl).

[0098] d. Prepare a casting solution with a mass fraction of 12% by mixing the product (SEBS-g-PSt@CH2Cl) and N,N-dimethylformamide. Allow it to stand until it reaches a certain viscosity and flowability. Vacuum the solution for 20 minutes to remove bubbles. Apply the solution to a polyacrylonitrile filter membrane using a doctor blade. Set the membrane at room temperature for 3 hours, then vacuum dry it at 80°C for 12 hours. Immerse the plate in deionized water to remove the membrane (SEBS-g-PSt@CH2Cl) and dry it.

[0099] e. Cut the dried SEBS-g-PSt@CH2Cl membrane, add triethylamine solution (quaternizing agent) at a mass ratio of 1:20, seal, and react at room temperature for 48 hours; then immerse the membrane in 1 mol L... -1 The membrane was removed and dried in a sodium hydroxide solution to obtain a grafted chloromethylated SEBS pervaporation membrane.

[0100] In another embodiment of the present invention, a positively charged side-chain alkyl-grafted membrane C is provided. n The preparation method of SEBS includes the following steps:

[0101] a. This step is the same as step a in the first embodiment, except that steps b, c, d, and e are replaced by step b1.

[0102] b1. Prepare a polymer solution with a mass fraction of 5-25% by adding 75-85 parts of the chloromethylated product (SEBS@CH2Cl) to chloroform. Stir until completely dissolved under a nitrogen atmosphere. Then add 15-25 parts of alkylamine reagent (N,N-dimethylbutylamine, N,N-dimethyloctylamine, N,N-dimethyldodecylamine, or N,N-dimethyl-1-hexadecylamine) and perform a grafting reaction at 25-55°C for 6-48 hours. Subsequently, cast the mixture onto a substrate (glass, polytetrafluoroethylene (PTFE) plate, polyethyleneimine (PEI) filter membrane, polysulfone filter membrane, polyethersulfone filter membrane, nylon filter membrane, polyacrylonitrile filter membrane, cellulose acetate filter membrane) and allow the solvent to evaporate. After the membrane is formed, place the plate in a vacuum oven to dry for 24-72 hours, then immerse it in deionized water, remove the membrane and dry it to constant weight to obtain the final product.

[0103] Using the chloromethylated product of SEBS as a raw material, long side chains containing hydrophilic quaternary ammonium groups are introduced in one step at the chloromethyl sites of the styrene block via grafting. By generating hydrophilic quaternary ammonium groups in situ on the side chains, the permeability of the membrane to water molecules can be improved, and a microphase separation structure can be formed to regulate the diffusion performance of water molecules within the membrane. Simultaneously, the long hydrophobic chains contained in the grafted side chains make the hydrophilic / hydrophobic microphase separation structure of the membrane more pronounced. The hydrophobic regions within the membrane accelerate the aggregation to form continuous, large-area hydrophobic water zones, indirectly promoting the aggregation of hydrophilic regions to form equally large continuous hydrophilic water zones. By strengthening the microphase separation structure of the membrane, the nanochannels for water molecule transport are broadened, further promoting water molecule transport within the membrane and enhancing the membrane's pervaporation and desalination performance. Furthermore, the introduction of long chains can also provide SEBS with a certain degree of flexibility, avoiding gelation during the reaction process.

[0104] The present invention will be further illustrated below with reference to specific embodiments.

[0105] Example 6

[0106] a. The steps are the same as step a in Example 1.

[0107] b1. Take 75 parts of SEBS@CH2Cl and add it to chloroform to prepare a 15% (w / w) polymer solution. After complete dissolution by stirring under a nitrogen atmosphere, add 25 parts (w / w) of N,N-dimethylbutylamine and react at 30°C for 8 hours. Then, cast the mixture onto a polytetrafluoroethylene (PTFE) flat sheet polyethersulfone (PES) filter membrane and allow the solvent to evaporate. After membrane formation, place the flat sheet in a vacuum oven and dry for 48 hours. Then, immerse it in deionized water, remove the membrane, and dry it to constant weight to obtain the final product.

[0108] Example 7

[0109] a. The steps are the same as step a in Example 1.

[0110] b1. Take 85 parts of SEBS@CH2Cl and add it to chloroform to prepare a 25% (w / w) polymer solution. After complete dissolution by stirring under a nitrogen atmosphere, add 15 parts (w / w) of the alkylamine reagent N,N-dimethyldodecylamine and react at 55°C for 6 hours. Then, cast the mixture onto a cellulose acetate filter membrane and allow the solvent to evaporate. After membrane formation, place the plate in a vacuum oven and dry for 24 hours. Then immerse it in deionized water, remove the membrane, and dry it to constant weight to obtain the final product.

[0111] Example 8

[0112] a. The steps are the same as step a in Example 1.

[0113] b1. Take 80 parts of SEBS@CH2Cl and add it to chloroform to prepare a 5% (w / w) polymer solution. After complete dissolution by stirring under a nitrogen atmosphere, add 20 parts (w / w) of the alkylamine reagent N,N-dimethyl-1-hexadecylamine and react at 25°C for 48 hours. Then, cast the mixture onto a polytetrafluoroethylene (PTFE) plate and allow the solvent to evaporate. After membrane formation, place the plate in a vacuum oven and dry for 72 hours. Then immerse it in deionized water, remove the membrane, and dry it to constant weight to obtain the final product.

[0114] A third embodiment of the present invention provides a method for preparing a positively charged alkyl-grafted crosslinked membrane CL-SEBS, comprising the following steps:

[0115] a. This step is the same as step a in the first embodiment, except that steps b, c, d, and e are replaced by step b2.

[0116] b2. Add 79–83 parts of the chloromethylated product (SEBS@CH2Cl) to chloroform to prepare a polymer solution with a mass fraction of 5–25%, and stir until completely dissolved. Then add 14–16 parts of allylamine reagent (diallylamine, triallylamine, N,N-dimethylallylamine, or N-methylallylamine), and perform the grafting reaction at 25–55°C for 6–48 h. Subsequently, 3–5 parts of crosslinking agent (o-phenylenediol, 1,4-benzene-dithiol, biphenyl-4,4′-dithiol, 1,5-pentanedithiol, 1,6-hexanedithiol, or 3,6-dioxo-1,8-octanedithiol) are added and stirred for 10–30 min. The mixture is then cast onto a substrate (glass, polytetrafluoroethylene (PTFE) flat plate, polyethyleneimine (PEI) filter membrane, polysulfone filter membrane, polyethersulfone filter membrane, nylon filter membrane, polyacrylonitrile filter membrane, cellulose acetate filter membrane). After the membrane on the substrate has set, it is placed in an oven and subjected to a crosslinking reaction at 100–150 °C for 3–12 h to obtain a crosslinked grafted chloromethylated SEBS pervaporation membrane.

[0117] Using the chloromethylated product of SEBS as raw material, olefin functional groups and hydrophilic quaternary ammonium groups are introduced in one step through grafting to the chloromethyl sites of the styrene block. The introduction of side-chain hydrophilic groups can enhance the microphase separation structure of the membrane. Traditional pervaporation membrane materials suffer from swelling due to increased hydrophilicity, leading to a decrease in the membrane's salt retention capacity. Therefore, an olefin structure is introduced to the SEBS side end, and a crosslinked structure is constructed within the membrane using a crosslinking agent containing thiol functional groups through a click chemistry "ene-thiol" crosslinking reaction. The CS bond constructed with "ene-thiol" has a larger bond energy than the uncrosslinked structure and the ionic crosslinked structure, thus exhibiting higher swelling resistance and stability. The introduction of a three-dimensional crosslinked network gives the membrane higher mechanical strength and dimensional stability. This allows the membrane to maintain high selectivity while possessing hydrophilicity, avoiding the "trade-off" effect between membrane permeability and selectivity caused by enhanced hydrophilicity, enabling the membrane to operate stably in pervaporation devices for a long time.

[0118] The present invention will be further illustrated below with reference to specific embodiments.

[0119] Example 9

[0120] a. The steps are the same as step a in Example 1.

[0121] b2. 79 parts of SEBS@CH2Cl were added to chloroform to prepare a 15% (w / w) polymer solution. After complete dissolution, 16 parts (w / w) of N,N-dimethylallylamine were added, and the mixture was reacted at 30°C under a nitrogen atmosphere for 12 hours. Subsequently, 5 parts (w / w) of 1,4-benzene-dithiol were added, and the mixture was stirred for 30 minutes. The mixture was then cast onto a polytetrafluoroethylene (PTFE) plate. After the film on the plate was set, it was placed in an oven and heated under vacuum at 100°C for 12 hours to obtain a crosslinked CL-SEBS membrane.

[0122] Example 10

[0123] a. The steps are the same as step a in Example 1.

[0124] b2. Take 80 parts of SEBS@CH2Cl and add it to chloroform to prepare a 5% (w / w) polymer solution. After it is completely dissolved, add 15 parts (w / w) of N-methylallylamine and react it at 25°C under a nitrogen atmosphere for 6 hours. Then add 5 parts (w / w) of o-phenylenediol and stir for 15 minutes. Cast the mixture onto a glass plate. After the film on the plate has set, place it in an oven and react it under vacuum at 150°C for 8 hours to obtain a crosslinked CL-SEBS film.

[0125] Example 11

[0126] a. The steps are the same as step a in Example 1.

[0127] b2. Take 83 parts of SEBS@CH2Cl and add it to chloroform to prepare a 20% (w / w) polymer solution. After it is completely dissolved, add 14 (w / w) of diallylamine and react it at 45°C under a nitrogen atmosphere for 30 hours. Then add 3 (w / w) of 1,5-pentanedithiol and stir for 20 minutes. Cast the mixture onto a polyethyleneimine (PEI) filter membrane. After the membrane on the plate is set, place it in an oven and react it under vacuum at 100°C for 5 hours to obtain a crosslinked CL-SEBS membrane.

[0128] Example 12

[0129] a. The steps are the same as step a in Example 1.

[0130] b2. Take 81 parts of SEBS@CH2Cl and add it to chloroform to prepare a 25% (w / w) polymer solution. After it is completely dissolved, add 14 parts (w / w) of triallylamine and react it at 55°C under a nitrogen atmosphere for 48 hours. Then add 5 parts (w / w) of 3,6-dioxo-1,8-octanedithiol and stir for 10 minutes. Cast the mixture onto a polysulfone filter membrane. After the membrane on the plate is set, place it in an oven and react it under vacuum at 120°C for 3 hours to obtain a crosslinked CL-SEBS membrane.

[0131] Simulated seawater desalination experiments were conducted using Examples 1-12, with the following specific experimental conditions:

[0132] The prepared membrane was placed in a pervaporation test chamber, with an effective membrane area of ​​15.9 cm². -2 The feed rate is 16L / h. -1 Feed solutions at different temperatures (45 or 65°C) and at different concentrations (5 wt% or 20 wt%) are transported from the feed tank to the membrane surface via the feed-side conveying system. The permeate side is under vacuum. Water molecules permeate through the membrane and are condensed and collected as water vapor to obtain fresh water.

[0133] Comparative Example 1: CTA / Al2O3 nanocomposite film

[0134] The pervaporation desalination membrane used in this example is an inorganic / inorganic composite membrane material prepared from inorganic materials cellulose triacetate (CTA) and Al2O3.

[0135] Comparative Example 2: PVA-SiO2 / polysulfone hybrid film

[0136] The pervaporation desalination membrane used in this example is an organic / inorganic hybrid membrane prepared by solvent blending of organic material polyvinyl alcohol (PVA) and inorganic material SiO2 with a polysulfone ultrafiltration membrane.

[0137] Comparative Example 3: Sulfonated SEBS (S-SEBS) membrane

[0138] The pervaporation desalination membrane used in this example is an organic block polymer membrane material prepared by sulfonation using SEBS, the same block polymer material as in this invention.

[0139] Table 1 lists a comparison of the pervaporation desalination performance of Examples 1-12 and Comparative Examples 1-3 above, to illustrate the advantages of the grafted / crosslinked modified block polymer membrane.

[0140] Table 1. Performance Comparison of Grafted / Crosslinked Modified Block Polymer Membranes

[0141]

[0142] This invention uses polystyrene-(ethylene / butene)-styrene block polymers as raw materials (e.g.) Figure 1 As shown in the figure, this block polymer has rigid styrene blocks and flexible ethylene / butene blocks, thus exhibiting both excellent thermal / chemical stability and film-forming properties. Figure 2 The image shows the grafted chloromethylated SEBS pervaporation membrane prepared in Example 4. Quaternization hydrophilic modification modifies the hydrophilic / hydrophobic properties between the styrene and ethylene / butene blocks of the membrane, facilitating the formation of a microphase separation structure within the membrane and enabling rapid, low-energy-barrier transport of water molecules. The grafted styrene blocks also contribute to improving the membrane's mechanical strength and dimensional stability. Figure 3 and Figure 4 The NMR spectra of SEBS and chloromethylated SEBS are shown below. Observation and comparison revealed a new peak near the chemical shift δ = 4.6 ppm, which is a signal generated by the hydrogen resonance of the chloromethyl peak introduced on the benzene ring, indicating the successful occurrence of the chloromethylation reaction. Furthermore, by introducing hydrophilic quaternary ammonium groups in a one-step manner through alkyl side chains and regulating the microphase separation structure of the membrane, the physicochemical properties of the membrane are altered, widening the nanoscale channels for water molecule transport and facilitating water molecule transport within the membrane. Simultaneously, to avoid membrane swelling and decreased mechanical strength and selectivity caused by high hydrophilicity, a thiol crosslinking agent is introduced based on the alkylamine side chain structure to construct an olefin-thiol crosslinking reaction, introducing a three-dimensional crosslinked network into the membrane. This enhances the membrane's mechanical properties and anti-swelling properties, avoiding the "trade-off" effect between membrane permeability and selectivity.

[0143] To compare the desalination performance of different types of pervaporation membrane materials, experimental characterization tests were conducted on side-chain alkyl-grafted membranes and alkyl-grafted crosslinked membranes. The results are listed in Table 1. Compared with Comparative Examples 1 and 2, the prepared grafted chloromethylated SEBS pervaporation membrane had several times the pervaporation water flux, and its salt rejection rate was also one quantile higher. Compared with Comparative Example 3 prepared from the same type of material, the pervaporation flux of Example 1 at a low feed temperature of 45°C was 19.87 kg·m³. -2 ·h -1 Slightly lower than the 22.87 kg·m of Comparative Example 3. -2 ·h -1 However, considering the calorific value cost of heating the feed liquid, it indicates that Example 1 can achieve desalination performance close to that of Comparative Example 3 under low-temperature feed conditions. Meanwhile, Example 2, when faced with 20wt% high-concentration brine, achieves 18.93 kg·m³. -2 ·h -1 The flux was similar to that of Example 1 and Comparative Example 3, and significantly higher than that of Comparative Example 1 (6.71 kg·m³). -2 ·h -1 ) and Comparative Example 2 (10.42 kg·m -2 ·h -1 This demonstrates the advantage of Example 2 when dealing with high-concentration feeds. Compared to Comparative Example 3 and Example 1, the pervaporation water flux of Examples 3-5, which increased the feed temperature, was 18-19 kg·m³. -2 ·h -1 Increased to 28-29 kg·m -2 ·h -1 Furthermore, the salt rejection rate remains at approximately 99.97%. This demonstrates that the pervaporation membrane of the first embodiment possesses excellent pervaporation desalination capability, maintaining high performance under both low-temperature and high-concentration conditions compared to pervaporation membranes made of conventional materials. In addition, compared to the five embodiments of the first embodiment, Examples 6-8 of the second embodiment have a flux of 28 kg·m³. -2 ·h -1 Increased to 30 kg·m -2 ·h -1 While the membrane's salt retention capacity and mechanical strength decreased to some extent, the introduction of long hydrophobic side chains made the microphase separation structure within the membrane more pronounced. This resulted in the formation of continuous hydrophilic water zones, enhancing the transport performance of water molecules within the membrane and causing a degree of swelling, allowing some salt ions to permeate into the membrane. Examples 9-12 of the third embodiment address these issues by constructing a three-dimensional crosslinked network (such as an olefin-thiol click crosslinking method) within the membrane. Figure 5As shown in the figure, different polymer chains are linked by covalent bonds, which increases the mechanical strength of the membrane from 11-12 MPa in Examples 6-8 to about 28 MPa, greatly enhancing the dimensional stability of the membrane. At the same time, the introduction of the cross-linked structure slightly reduces the pervaporation flux of the membrane, but it still remains at 25 kg·m³. -2 ·h -1 The membrane exhibits a high permeability and selectivity, with a salt rejection rate maintained at around 99.97%, achieving a balance between the two and avoiding their mutual constraints. Furthermore, the cross-linked structure of Examples 9-12 allows for long-term stable operation of the membrane and makes it more likely to be applied in industrial processes.

[0144] This membrane can be used in the pervaporation desalination process of seawater and high-salinity wastewater. The membrane is dense and contains a large number of positively charged quaternary ammonium groups, which is beneficial to improve the membrane's ability to retain salt ions based on charge repulsion. At the same time, it utilizes its excellent microbial degradation ability to inhibit the deposition of microorganisms on the membrane surface and alleviate membrane fouling. It has promising applications in seawater desalination, brackish water desalination, and industrial wastewater treatment. This high-flux, high-selectivity, and high-stability pervaporation membrane can also serve as a potential membrane material in fields such as water electrolysis for hydrogen production, microbial fuel cells, and energy storage. It has advantages such as antifouling, low cost, high operational stability, and environmental friendliness, and can be applied in alkaline fuel cells, wastewater electrodialysis, and electrodeionization.

[0145] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a grafted chloromethylated SEBS pervaporation membrane, characterized by, Comprising: a. 5-10 parts of block polymer is prepared into polymer solution A, 10-20 parts of chloromethylation reagent is added and stirred to dissolve; 50-60 parts of trimethylchlorosilane and 15-25 parts of catalyst A are added under ice water bath condition for reaction; The block polymer is one of polystyrene-(ethylene / butylene)-styrene or styrene; The catalyst A is anhydrous zinc chloride, anhydrous ferric chloride, anhydrous aluminum chloride or anhydrous tin tetrachloride; Methanol / water mixed precipitation to obtain the product, purification, drying to obtain chloromethylated product SEBS@CH2Cl; b. 25-30 parts of product SEBS@CH2Cl is prepared into polymer solution B; 60-70 parts of monomer, 2-5 parts of catalyst B and 3-6 parts of ligand are added and mixed to dissolve; The monomer is styrene or maleic anhydride; The catalyst B is copper chloride, copper bromide, nickel chloride, ferric chloride hexahydrate or nickel chloride hexahydrate; The ligand is iminodiacetic acid, tris[2-(dimethylamino)ethyl]amine, triphenylphosphine or tri-n-butylamine; 1-5 parts of reducing agent is added in liquid nitrogen vacuum atmosphere for reaction; The reducing agent is tin(II) 2-ethylhexanoate or ascorbic acid; Methanol precipitation to obtain the product, drying to obtain polystyrene graft product SEBS-g-PSt; c. 5-10 parts of graft product is prepared into polymer solution C, 10-20 parts of chloromethylation reagent is added and stirred to dissolve; 50-60 parts of trimethylchlorosilane and 15-25 parts of catalyst A are added under ice water bath condition for reaction; Methanol / water mixed precipitation to obtain the product, purification, drying to obtain chloromethylated graft product SEBS-g-PSt@CH2Cl; d. The chloromethylated graft product SEBS-g-PSt@CH2Cl is prepared into casting solution, standing, vacuum defoaming; The casting solution is coated on the substrate, and is shaped at room temperature, vacuum drying, and the chloromethylated graft membrane is taken out in water, drying; e. The chloromethylated graft membrane is reacted with quaternary ammonium reagent, immersed in lye, and a graft type chloromethylated SEBS pervaporation membrane is formed.

2. The method for preparing a grafted chloromethylated SEBS pervaporation membrane according to claim 1, characterized in that, The solvent of the casting solution is toluene, chloroform, tetrahydrofuran, N-methyl pyrrolidone or N,N-dimethylformamide; The quaternary ammonium reagent is trimethylamine solution, triethylamine solution or tributylamine solution.

3. The method of producing a grafted chloromethylated SEBS pervaporation membrane according to claim 1, characterized by, In steps a and c, the reaction is carried out under ice water bath condition for 10-60 min, and the ice water bath is removed and the reaction is carried out at 25-55℃ for 6-24 h; In step b, after nitrogen is passed, the reducing agent is added by slowly heating to 80-120℃; the reaction is carried out at 80-120℃ and in nitrogen atmosphere for 6-12 h.

4. A method for producing a grafted chloromethylated SEBS pervaporation membrane, characterized by, Comprising: a. 5-10 parts of block polymer is prepared into polymer solution A, 10-20 parts of chloromethylation reagent is added and stirred to dissolve; 50-60 parts of trimethylchlorosilane and 15-25 parts of catalyst A are added under ice water bath condition for reaction; The block polymer is one of polystyrene-(ethylene / butylene)-styrene or styrene; The catalyst A is anhydrous zinc chloride, anhydrous ferric chloride, anhydrous aluminum chloride or anhydrous tin tetrachloride; Methanol / water mixed precipitation to obtain the product, purification, drying to obtain the chloromethylation product SEBS@CH2Cl; b1. 75-85 parts of chloromethylated product SEBS@CH2Cl are prepared into a polymer solution D, 15-25 parts of alkyl amine reagent are added to react under nitrogen atmosphere, the mixture is cast on a substrate, and after volatilization to form a film, drying, immersion in deionized water, the film is taken out and dried to obtain a grafted chloromethylated SEBS pervaporation membrane.

5. The method of producing a grafted chloromethylated SEBS pervaporation membrane according to claim 4, characterized by, The alkyl amine reagent is N,N-dimethylbutylamine, N,N-dimethyloctylamine, N,N-dimethyldodecylamine or N,N-dimethyl-1-hexadecylamine; In step a, the reaction is carried out under ice water bath for 10-60 min, and after removing the ice water bath, the reaction is carried out at 25-55℃ for 6-24 h; In step b1, the grafting reaction is carried out at 25-55℃ for 6-48 h.

6. A method for preparing a grafted chloromethylated SEBS pervaporation membrane, characterized by, It comprises: a. 5-10 parts of block polymer are prepared into a polymer solution A, and 10-20 parts of chloromethylation reagent are added to stir and dissolve; 50-60 parts of trimethylchlorosilane and 15-25 parts of catalyst A are added to react under ice water bath; The block polymer is one of polystyrene-(ethylene / butylene)-styrene or styrene; The catalyst A is anhydrous zinc chloride, anhydrous ferric chloride, anhydrous aluminum chloride or anhydrous stannic chloride; Methanol / water mixed precipitation to obtain the product, purification, drying to obtain the chloromethylation product SEBS@CH2Cl; b2. 79-83 parts of chloromethylated product SEBS@CH2Cl are prepared into a polymer solution E, 14-16 parts of allyl amine reagent are added, and 3-5 parts of crosslinking agent are added, the mixture is cast on a substrate, and after film shaping, a grafted chloromethylated SEBS pervaporation membrane is obtained.

7. The method of producing a grafted chloromethylated SEBS pervaporation membrane according to claim 6, characterized by, The allyl amine reagent is diallylamine, triallylamine, N,N-dimethylallylamine or N-methylallylamine; The crosslinking agent is o-phenylenedithiol, 1,4-benzene-dithiol, diphenyl-4,4'-dithiol, 1,5-pentanedithiol, 1,6-hexanedithiol or 3,6-dioxo-1,8-octanedithiol; In step a, the reaction is carried out under ice water bath for 10-60 min, and after removing the ice water bath, the reaction is carried out at 25-55℃ for 6-24 h; In step b2, the grafting reaction is carried out at 25-55℃ for 6-48 h, and the crosslinking reaction is carried out at 100-150℃ for 3-12 h.

8. The preparation method of the grafted chloromethylated SEBS pervaporation membrane according to any one of claims 1, 4 or 6, characterized in that The chloromethylation reagent is chloromethyl ether, trioxane, polyoxymethylene or methylal; The substrate is glass, polytetrafluoroethylene, polyethyleneimine filter membrane, polysulfone filter membrane, polyethersulfone filter membrane, nylon filter membrane, polyacrylonitrile filter membrane or cellulose acetate filter membrane.

9. A grafted chloromethylated SEBS pervaporation membrane prepared by the method according to any one of claims 1-7.

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